Neutral Ring for Use in Rotating Electrical Machine and Method for Manufacturing the Same

ABSTRACT

A rotating electrical machine includes a rotor core, a rotor shaft, a coil, a bind, a lead-out wire of which one end is connected to the coil and the other end is connected to a neutral ring. A filling is filled between the coil and the neutral ring. The neutral ring is formed with a plurality of members that are connected with one another to have flexibility.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Japanese PatentApplication No. 2014-162022, filed on Aug. 8, 2014, the entirespecification, claims and drawings of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a neutral point (neutral ring) for usein a rotor of a rotating electrical machine and a method formanufacturing the same.

2. Description of the Related Arts

Field coils of a rotor of a rotating electrical machine usingthree-phase AC are arranged with a neutral point called as a neutralring for shunting respective phase coils. In general, the neutral ringis a ring-shaped member made of metal such as copper and an aluminumalloy having a favorable electrical property of a resistance or thelike, and connected to one ends of respective phase coils to constitutea star connection of three-phase coils.

When the rotor rotates, the neutral ring receives stress due tocentrifugal force by rotation. In addition, junctions between the coilsand the neutral ring also receive stress due to deformation ofrespective phase coils.

If the amplitude of fluctuations is large in rotation speed of therotating electrical machine or fluctuations occur many times, theabove-mentioned stress increases or the stress occurs many times.Accordingly, the neutral ring may suffer fatigue breakdown. Once theneutral ring suffers the fatigue breakdown, the rotor cannot generate amagnetic field and the rotating electrical machine loses its function.Consequently, it is essential to reduce the stress on the neutral ringfor providing a rotating electrical machine having a long service life.

Techniques concerning a neutral ring have been described, for example,in Japanese Patent Application Publication No. S63-249440 and JapaneseUtility Model Application Publication No. S51-121701. In the formerreference, the neutral ring is arranged in the ring-shaped rigid bodythat is supported by and fixed to a rotor end plate at an end of themagnetic core of the rotor. In the latter reference, the neutral ring isembedded into and supported by a support of the coils of the rotor.

SUMMARY OF THE INVENTION

However, the techniques described in the above references employ theneutral ring that is a ring-shaped rigid body. When a deformationdifference between the neutral ring and the coils due to centrifugalforce caused by rotation of the rotor increases, the stress at thejunctions between the neutral ring and the coils becomes larger, tocause fatigue damage to be accumulated in the junctions.

In an aspect of the invention, the present invention provides a neutralring that reduces stress due to the deformation difference and preventsfatigue damage from being accumulated and a method of manufacturing theneutral ring in which a related neutral ring can be altered to theneutral ring of the present invention.

To solve the problem mentioned above, in the present invention, aneutral ring is not a rigid body in a ring shape but is formed with aplurality of arc-shaped members that are connected with one another tohave a flexible structure so as to follow deformation of a coil. Theneutral ring of the present invention is formed with the plurality ofarc-shaped members that are connected with one another being overlappedin a circumferential direction to have less rigidity as compared withthe ring shape.

Since the neutral ring having low rigidity can easily follow deformationof the coils due to centrifugal force, the junctions between the coilsand the neutral ring do not receive large stress. As a result, thefatigue damage on the neutral ring can be reduced to allow for extendingthe service life of the neutral ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of an embodiment accordingto the present invention;

FIG. 2 is a cross sectional view as viewed from a direction of a rotorshaft of the embodiment according to the present invention;

FIG. 3 is a cross sectional view as viewed from the direction of therotor shaft of the embodiment according to the present invention;

FIG. 4 is a cross sectional view of a neutral ring according to arelated art;

FIG. 5 is a view showing a member of the neutral ring according to theembodiment of the present invention;

FIG. 6 is an explanatory view showing effects of the present invention;and

FIG. 7 is an explanatory view showing the effect of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described with referenceto FIGS. 1 to 5.

FIG. 1 is a partial cross sectional view in which an upper half of arotor 1 in a rotating electrical machine is cut out in an axis directionto show a main part of the present invention. FIG. 2 is a crosssectional view as viewed from the axis direction to show the main partof the rotor 1.

The rotor 1 includes: a rotor core 9; a core back 10 that fixes therotor core 9 to a rotor shaft 13; a rotor clamp 11; a key 12; a coil 3including a K-phase coil 3 a, an L-phase coil 3 b, an M-phase coil 3 cthat penetrates into the rotor core 9; a bind 2 that receivescentrifugal force of the coil 3; and a K-phase lead-out wire 4 a, anL-phase lead-out wire 4 b, an M-phase lead-out wire 4 c that areconnected to the coil 3 (one end of each lead-out wire is connected tothe coil 3 and the other end thereof is connected to a neutral ring 6including neutral ring members 6 a, 6 b and 6 c, to connect the coil 3to the neutral ring 6). An insulator 7 made of glass cloth, mica, epoxyor the like is filled between the coil 3 and the neutral ring 6.

As shown in FIG. 2, the neutral ring members 6 a, 6 b and 6 c areconnected to the K-phase coil 3 a, the L-phase coil 3 b and the M-phasecoil 3 c of each phase, respectively. In a case where the rotor 1 isdriven by three-phase AC or generates three-phase AC as the rotatingelectrical machine, the coils 3 a, 3 b, 3 c for three phases arearranged to include certain angles in a rotation direction of the rotor1 as the k-phase coil 3 a, the L-phase coil 3 b and the M-phase coil 3c.

A neutral point of the K-phase coil 3 a is connected to the the K-phaseneutral ring member 6 a via the K-phase lead-out wire 4 a with a K-phasebrazing 5 a or the like. The same applies to respective connections ofthe L-phase coil 3 b and the M-phase coil 3 c to the L-phase neutralring member 6 b and the M-phase neutral ring member 6 c.

The neutral ring members 6 a, 6 b, 6 c of respective phase are membersobtained by forming elongated conductive plates having low resistance,such as copper and aluminum alloy in an arc shape. The arc-shapedneutral ring members 6 a, 6 b, 6 c for respective phases are overlappedin a circumferential direction and connected at respective connectionpoints 14 a, 14 b, 14 c by brazing or the like. This forms the neutralring 6 that serves as the neutral point for each phase coil.

The neutral ring members 6 a, 6 b, 6 c for respective phases arearranged outermost at places where those are connected to the coils 3 a,3 b, 3 c for respective phases. As the neutral ring members 6 a, 6 b, 6c extend in the circumferential direction (clockwise direction in FIG.2), respective neutral ring members are placed at more innercircumference sides. Then, at respective positions of the lead-out wires4 a, 4 b, 4 c for adjacent phases, respective neutral ring members arelocated at second inner positions from the outermost. If the respectiveneutral ring members 6 a, 6 b, 6 c are long enough to pass throughanother lead-out wires 4 a, 4 b, 4 c, respective neutral ring membersare located at the third inner positions from the outermost.

In FIG. 2, the K-phase neutral ring member 6 a has an arc shape. Withthe position of the K-phase lead-out wire 4 a, which is a connectionpoint with the K-phase coil 3 a, being assumed as a starting point ofthe arc, the arc ending at an end of the K-phase neutral ring member 6 asubtends a central angle C. With the same central angle definition, in adirection to which the K-phase neutral ring 6 a extends, arcs ending atthe M-phase lead-out wire 4 c and the L-phase lead-out wire 4 b subtenda central angle A and a central angle B, respectively.

The embodiment shown in FIG. 2 satisfies the formula 1 below.

C≧B>A  [formula 1]

By satisfying the formula 1, the neutral ring members 6 a, 6 b, 6 c areformed to be ring springs cut in part. Therefore, the neutral ringmembers 6 a, 6 b, 6 c have low rigidity against a load in a radialdirection to easily follow deformation of the coils 3 a, 3 b, 3 c andthe lead-out wires 4 a, 4 b, 4 c in the radial direction. Thus, stresscaused by the deformation of the coils 3 a, 3 b, 3 c and the lead-outwires 4 a, 4 b, 4 c in the radial direction which the neutral ringmembers 6 a, 6 b, 6 c receive can be reduced. In addition, though beingdifferent from FIG. 2, a structure that satisfies the formula 2 belowcan obtain approximately the same effect.

B>C≧A  [formula 2]

In this case, the neutral ring 6 is formed in double layers to allow forreducing a mass of the neutral ring 6.

The neutral ring members 6 a, 6 b, 6 c may be formed in double layers ortriple layers. At this time, each of the neutral ring members 6 a, 6 b,6 c is arranged as a single body entity with an insulator 8 such as aglass tape and a resin tape, and is connected to each of the connectionpoints 14 a, 14 b, 14 c by brazing or the like. Alternatively, each ofthe neutral ring members 6 a, 6 b, 6 c may be not insulated as a singlebody entity but lashed with the glass tape for integration. In addition,overlapping portions of respective neutral ring members 6 a, 6 b, 6 cmay have resin to slide with each other. In the same manner, the neutralring members 6 a, 6 b, 6 c may not be connected by brazing or the likeat the connection points 14 a, 14 b, 14 c, but may be contacted bylashing connection or by a structure such as a pin, a bolt or a dovetailgroove with which the connection points and the neutral ring members canslide to each other.

Referring to FIGS. 3 and 4, a method of manufacturing the neutral ringmembers 6 a, 6 b, 6 c (FIG. 3) in the embodiment of the presentinvention will be explained.

This method shows how the neutral ring members 6 a, 6 b, 6 c shown inFIG. 3 are formed by altering the related neutral ring 15 (FIG. 4). FIG.4 shows a neutral ring of a related art. In the related art, a neutralring 15 has a ring shape. Other structures are approximately the same asthose described in FIG. 2.

The K-phase neutral ring member 6 a will be described as an example ofalteration. At first, the neutral ring 15 is separated from theinsulator 7. Since being adhered or lashed by the glass tape or the liketo the insulator 7, the neutral ring 15 is separated by cutting off theglass tape or the like. At this time, the insulator 7 should not bebroken, nor removed to a large extent.

Then, the neutral ring 15 is cut off in part from a cutting position 15a to a cutting position 17 a. The cutting position 15 a is around thebrazing 5 a between the lead-out wire 4 a and the neutral ring 15 butdoes not affect the connection by the brazing 5 a. In this example, thecutting position is located at the left side of the brazing 5 a. Thecutting position 17 a is located between the K-phase and L-phase coilswhere jumper wires and/or lead wires to an outside of the rotor are notinterrupted. Further, the cutting position 17 a is located away from theL-phase coil to allow the neutral ring 15 to have sufficient flexibilityafter the neutral ring 15 is cut off. Cutting off the ring at a positionto allow the ring to have flexibility facilitates connecting the neutralrings to be described later. In the same manner as the cutting positionsfor K-phase neutral ring, the respective cutting positions 15 b, 17 b,and cutting positions 15 c, 17 c of the L-phase and M-phase coils arepositions offset from positions of the K-phase coil by amount ofdistance between respective two coils.

Next, new connection elements 18 of the neutral ring in an arc shape(FIG. 5) are connected at the cutting positions 17 a, 17 b, 17 c of theneutral ring, respectively. In a case of the K-phase coil 3 a, one end19 of the connection element 18 is connected at the cutting position 17c by brazing or the like. A connection portion may be formed with abevel to enhance strength. As a result of the connection, as shown inFIG. 3, the K-phase neutral ring member 6 a is connected to theconnection element 18 via the connection portion 16 a to form a k-phaseneutral ring 21 a by the connection. The same applies to the connectionelements 18 to the L-phase neutral ring member 6 b and M-phase neutralring member 6 c. Thus, the L-phase neutral ring member 6 b and M-phaseneutral ring member 6 b are connected to the connection elements 18 atconnection portions 16 b, 16 c to form neutral rings 21 b, 21 c,respectively.

The K-phase neutral ring 21 a is arranged along an inner circumferenceof the insulator 7, and is overlapped by the M-phase neutral ring member6 c around the lead-out wire 4 c of the M-phase coil 3 c. Accordingly,the K-phase neutral ring 21 a is arranged at an inner circumference sideof the M-phase neutral ring 21 c that is formed with the connectedM-phase neutral ring member 6 c. The other end 20 of the connectionelement 18 (FIG. 5) forms the connection point 14 a that is connected tothe inner circumference side of the neutral ring 21 c by brazing or thelike. The same applies to the L-phase neutral ring 21 b and M-phaseneutral ring 21 c that are connected to inner circumference sides of theK-phase neutral ring 21 a and L-phase neutral ring 21 b respectively viathe connection elements 18 by the same method as the K-phase neutralring 21 a.

The cutting portions of the neutral ring for each phase, that is, theregions between the cutting positions 15 a and 17 a, between the cuttingpositions 15 b and 17 b, and between the cutting positions 15 c and 17c, have gaps between the neutral rings 21 a, 21 b, 21 c and theinsulator 7 when the connection elements 18 are connected respectivelyas shown in FIG. 3. Therefore, insulators 22 a, 22 b, 22 c havingrelatively high rigidity such as glass cloth, mica, epoxy or the likeare filled in the gaps to prevent the neutral rings 21 a, 21 b, 21 cfrom being deformed by centrifugal force caused by the rotation of therotor.

In the present embodiment, the method shows how the neutral ring of thepresent invention can be formed from the related neutral ring. When theneutral ring is cut off to connect to the connection element, the lengthof the connection element is determined in consideration of rotorbalance. In some cases, balance weights in consideration of the rotorbalance may be placed in the regions where the insulators 22 a, 22 b, 22c are filled with.

Finally, advantages of the present invention are described withreference to FIGS. 6 and 7. FIGS. 6 and 7 show displacements δ1, δ2 inthe radial direction when arc-shaped members having central angles θ1,θ2 respectively are applied with external force F in the radialdirection. When radii r of the members are the same, if

central angle η1<central angle θ2   [formula 3]

is true, the following formula can be derived from calculations forbeams.

displacement δ1<displacement δ2  [formula 4]

Therefore, the neutral ring having a flexible structure can be obtainedby overlapping a plurality of arc-shaped members.

What is claimed is:
 1. A neutral ring for use in a rotating electrical machine including: a rotor coil; a rotor core; a bind that receives centrifugal force of the rotor coil; and a lead-out wire that extends from the rotor coil and of which one end is connected to the rotor coil and the other end is connected to the neutral ring, the neutral ring comprising a plurality of members in an arc shape that are connected with one another, wherein the neutral ring shunts the rotor coil in three phases and wherein a filling is filled between the rotor coil and the neutral ring.
 2. The neutral ring for use in the rotating electrical machine according to claim 1, wherein the plurality of members forming the neutral ring are overlapped with one another.
 3. The neutral ring for use in the rotating electrical machine according to claim 1, wherein the neutral ring extends with respect to a rotation shaft of a rotor.
 4. The neutral ring for use in the rotating electrical machine according to claim 2, wherein the neutral ring extends with respect to a rotation shaft of a rotor.
 5. A method for manufacturing a neutral ring for use in a rotating electrical machine, the rotating electrical machine including: a rotor coil; a rotor core; a bind that receives centrifugal force of the rotor coil; a lead-out wire that extends from the rotor coil and of which one end is connected to the rotor coil and the other end is connected to the neutral ring, the method comprising steps of: cutting off the neutral ring in part; connecting the cut-off neutral ring to an arc-shaped connection element; and filling an insulator between the cut-off neutral ring and the connection element, wherein the neutral ring shunts the rotor coil in three phases. 